What is the next term in the geometric sequence $$2, 6x, 18x^2, 54x^3, \ldots ?$$ Express your answer in terms of $x$.
Answer: The common ratio is $\frac{6x}{2} = 3x$; that is, each term is obtained by multiplying $3x$ to the previous term. The next term is thus $54x^3 \cdot 3x = \boxed{162x^4}$.